Problem: $ { {0} \times \left[\begin{array}{rr}{2} & {1} \\ {2} & {1}\end{array}\right] = {?} } $
To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{0}\times{2} & {0}\times{1} \\ {0}\times{2} & {0}\times{1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{0} & {0} \\ {0} & {0}\end{array}\right]}$